When a building is verticalized, a natural frequency of the building decreases, and therefore, when an earthquake occurs or a strong wind blows, a resonance phenomenon is likely to occur. When the natural frequency of the building and a natural frequency of a rope (such as a main rope, a compensating rope or a governor rope) of an elevator provided in a hoistway match, the rope is shaken greatly due to resonance. Hence, there is a concern that the rope contacts a device in the hoistway or a hoistway wall, and causes failure such as a catch of a rope.
To prevent this failure, a recent elevator first detects a shake of the building by means of a sensor installed in, for example, a machine room when the building is shaken. When the detected intensity and a continuation time exceed a certain threshold, a control operation is performed. That is, a passenger cage is moved to an evacuation floor (non-resonant floor), and operation service is stopped to prevent a catch of a rope. However, when a control operation is performed based only on the shake of the building and the continuation time of the shake, an elevator is stopped even though a rope is not actually shaken greatly, there is a concern that a stop frequency unnecessarily increases. Accompanying verticalization of buildings, a recent building adopts a structure which is easily shaken, and therefore, when the building is shaken by a wind, the control operation is launched every time and disturbs operation service.
Hence, Japan Patent No. 4399438 proposes an elevator device which, when a building is shaken by an earthquake or a strong wind, computes the amount of shake of a long object (such as a main rope, a compensating rope or a governor rope) in a hoistway according to a building shake signal, and controls and operates the elevator according to the result. With this elevator device, primary natural periods are different per shake in lateral and longitudinal directions of the building, and then a plurality of long object shake vibration models to which different natural periods (Ta, Tb, Tc: fixed values) are set are determined for the respective primary natural periods of the building and the amount of shake of the long object based on the building shake signal is computed per shake vibration model.
Further, upon an actual operation, a control operation of an elevator upon an earthquake and building shake control which is conventionally adopted are used in combination, and, even when a weak P wave first break caused by a long-period ground motion is missed, long object shake control is performed by S wave early sensing. That is, a long object shake grows over about 30 to 60 seconds after the S wave arrives, and a passenger cage is temporarily stopped at the nearest floor by S wave early control and the amount of shake of a long object is computed. An operation returns to a normal operation when a shake of the building is a little after a certain period of time and the long object is not shaken, and a control operation matching the amount of shake is performed when the long object is shaken.
Although this control is preferable to handle the earthquake, when a building is shaken by a strong wind, a passenger cage stops at the nearest floor due to a comparatively weak shake, and therefore it is difficult to decrease a stop frequency.
Further, upon computation of a shake of along object, natural periods of long object shake vibration models are fixed values Ta, Tb and Tc close to the primary natural period of the building, and assume a state where the shake of the long object is the greatest. The shake of the long object changes every second depending on a position of a passenger cage, and therefore it is not possible to calculate an accurate shake of the long object according to the vibration model which assumes a maximum shake at all times as described above.
Further, as another example, Japan Patent No. 4618101 also proposes an elevator control operation device which, when detecting a shake of a building due to an earthquake or a strong wind, predicts that various ropes of an elevator are caught by projections in a hoistway and transitions an operation to a control operation.
When a shake of a certain magnitude or more of a building occurs, this elevator control operation device temporarily stops the elevator and calculates the degree of a shake of each rope using, for example, building shake information or elevator cage position information. Further, the calculated degree of shake of the rope and a determination reference are compared to determine a likelihood of a catch of each rope and prevent the rope from being caught due to the operation of the elevator.
According to the above two examples, when a shake of a building is a certain magnitude or more, the operation of the elevator is first stopped and a shake of the rope (long object) is subsequently estimated, and therefore it is not possible to reduce a stop frequency of the elevator.